function objToString(obj) {
    var str = ''
    for (var key in obj) {
        str += `${key}=${obj[key]}&`
    }
    return str.slice(0, str.length - 1)

}
function ajax(method, url, mains) {
    return new Promise((resolve, reject) => {
        var xhr = new XMLHttpRequest()
        xhr.open(method, method == 'get' ? url + "?" + objToString(mains) : url)
        xhr.onreadystatechange = function () {
            if (xhr.readyState == 4) {
           resolve(JSON.parse(xhr.responseText))
            }
        }
        xhr.setRequestHeader('content-type', 'application/x-www-form-urlencoded')
        xhr.send(method == 'get' ? null : objToString(mains))
    })
}